Vacuum cleaner

ABSTRACT

The invention relates to a vacuum cleaner with a dirt collection tank which has a suction inlet and is in flow connection with at least one suction unit via at least one filter and at least one extraction line, and with at least one external air inlet which opens into the extraction line downstream of the at least one filter and can be closed by means of at least one closing valve, wherein the at least one closing valve has a valve member which can be moved back and forth between a closing position and an open position, wherein it is acted upon permanently by a closing spring with a closing force and in the closing position, in addition, by a magnetic holding device with a magnetic holding force. In order to develop the vacuum cleaner further in such a manner that it makes a particularly effective cleaning of the at least one filter possible, it is suggested in accordance with the invention that the magnetic holding device comprise an electromagnet with a magnetic core and a coil which can be acted upon with current for the purpose of closing the closing valve, wherein at least one electrical component, which takes up at least some of the energy stored in the coil when the current acting on the coil ceases, is connected in parallel to the coil.

This application is a continuation of International application No. PCT/EP2006/007541 filed on Jul. 29, 2006.

The present disclosure relates to the subject matter disclosed in International application No. PCT/EP2006/007541 of Jul. 29, 2006, which is incorporated herein by reference in its entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a vacuum cleaner with a dirt collection tank which has a suction inlet and is in flow connection with at least one suction unit via at least one filter and at least one extraction line, and with at least one external air inlet which opens into the extraction line downstream of the at least one filter and can be closed by means of at least one closing valve, wherein the at least one closing valve has a valve member which can be moved back and forth between a closing position, in which it abuts on a valve seat, and an open position, in which it is spaced from the valve seat, wherein it is acted upon permanently by a closing spring with a closing force and in the closing position, in addition, by a magnetic holding device with a magnetic holding force.

Dirt and, preferably, also liquid can be sucked up from a surface by means of such vacuum cleaners in that the dirt collection tank is acted upon with a vacuum with the aid of at least one suction unit so that a suction flow is formed and dirt and liquid can be sucked into the dirt collection tank. The vacuum cleaners have one or more filters which are arranged in the flow path between the dirt collection tank and the at least one suction unit and serve to separate solids from the suction flow. During suction operation, dirt particles are increasingly deposited on the side of the at least one filter facing the dirt collection tank and so the filter or filters need to be cleaned after a certain length of time. For the purpose of cleaning, the side of the filter facing away from the dirt collection tank can be acted upon with external air in that at least one closing valve is opened so that external air can flow into the at least one extraction line from the external air inlet and act upon the side of the at least one filter facing away from the dirt collection tank.

In the German Utility Model DE 298 411 U1, it is suggested for the purpose of cleaning a filter that a suction hose, which is connected to the suction inlet of the dirt collection tank, be closed for a short time so that a strong vacuum is formed in the dirt collection tank on account of the action of the suction unit and, subsequently, a closing valve is intended to be opened for a short time. The filter then has external air flowing through it in a counterflow direction, i.e., contrary to the direction of the suction flow prevailing during normal suction operation and so dirt particles adhering to the filter become detached.

The use of two filters, which are cleaned alternatingly, is suggested in DE 199 49 095 A1, wherein, during the cleaning of one filter, suction operation can be maintained via the other filter to a limited extent.

The object of the present invention is to develop a vacuum cleaner of the generic type further in such a manner that it makes a particularly effective cleaning of the at least one filter possible.

SUMMARY OF THE INVENTION

This object is accomplished in accordance with the invention, in a vacuum cleaner of the type specified at the outset, in that the magnetic holding device comprises an electromagnet with a magnetic core and a coil which can be acted upon with current for the purpose of closing the closing valve, wherein at least one electrical component, which takes up at least some of the energy stored in the coil when the current acting on the coil ceases, is connected in parallel to the coil.

In the case of the vacuum cleaner according to the invention, at least one closing valve is used, the valve member of which can be moved back and forth between a closing position and an open position. Irrespective of its position, the valve member is acted upon by a closing spring with a closing force in the direction of its closing position. In the closing position, the closing member is acted upon, in addition, by a magnetic holding force, with the aid of which it is ensured that the closed closing valve reliably closes the flow connection between the inlet for external air and the side of the filter facing away from the dirt collection tank. In this position, the normal suction operation of the vacuum cleaner takes place. If the at least one filter is intended to be cleaned, at least one closing valve is opened. In accordance with the invention, the closing valve has an electromagnet which can be acted upon with current for the purpose of closing the closing valve. For the purpose of opening the closing valve, the supply of current to the electromagnet is interrupted for a short time so that the holding force acting on the valve member ceases abruptly. During normal suction operation, the valve member is subject to a difference in pressure since the pressure of the external air, i.e., normally atmospheric pressure prevails on its side facing away from the filter whereas the vacuum of the extraction line is present at its side facing the filter. When the magnetic holding force ceases, this difference in pressure results in the valve member transferring into its open position contrary to the spring force of the closing valve. With increasing distance from the valve seat, which is associated with the valve member, the restoring force of the closing spring increases and so the valve member is returned to its closing position again by the closing spring. The opening of the closing valve results in the side of the filter, which faces away from the dirt collection tank, being acted upon with external air for a short time. This leads, on the one hand, to a pressure surge which mechanically jars the at least one filter; on the other hand, the at least one filter has external air flowing through it in a counterflow direction.

In order to bring about as abrupt an action on the filter with external air as possible, it is provided in accordance with the invention for the magnetic holding force to cease after as short a time as possible. For this reason, at least one electrical component, which takes up at least some of the energy stored in the coil when the current acting on the coil ceases, is connected in parallel to the coil. The coil forms a large inductivity for the electrical control circuit of the coil. When the supply of current is interrupted, the inductivity results in a high countervoltage on account of self-inductance. This countervoltage is short-circuited via the at least one electrical component connected in parallel to the coil, wherein this component takes up at least some of the energy stored in the coil. This makes it possible to return the magnetic field of the electromagnet, which prevails during normal suction operation, practically to zero within a very short period of time, preferably within less than 20 milliseconds, in particular, within a period of time of less than 10 milliseconds. The energy of the magnetic field will be taken up by the at least one electrical component connected in parallel to the coil when the supply of current to the coil is interrupted.

The use according to the invention of at least one electrical component which is connected in parallel to the coil and takes up at least some of the energy stored in the coil makes it possible for the magnetic holding force to drop practically to zero within a very short period of time. Subsequently, the electromagnet can again be acted upon with current so that the valve member, which has been returned to its closing position again by the closing spring, can be held sealingly on the valve seat by means of the renewed magnetic holding force.

The use according to the invention of at least one electrical component which is connected in parallel to the coil and takes up at least some of the energy stored in the coil when the supply of current to the coil is switched off therefore makes a very short opening of the closing valve possible. External air can, therefore, be supplied in an impact-like manner to the filter to be cleaned and can then also be discharged again immediately by the suction unit which is constantly in flow connection with the filter. The filter cleaning process is, therefore, carried out in fractions of a second. This has the advantage that there is no complete equalization of pressure between the vacuum prevailing in the dirt collection tank and the atmospheric pressure during the cleaning of the filter. On the contrary, a vacuum can also be maintained in the opening area of a suction hose connected to the suction inlet during the cleaning of the filter and so a more or less continuous suction operation results for the user despite the cleaning of the filter.

It is favorable when a freewheeling diode and at least one electrical component, which takes up energy and is connected in series thereto, are connected in parallel to the coil. The freewheeling diode ensures that an induced countervoltage at the coil is short-circuited. The freewheeling diode does, however, absorb only very little of the energy originally stored in the magnetic field of the electromagnet when the coil is short-circuited. Therefore, at least one electrical component which takes up energy is connected in series to the freewheeling diode. In this respect, an ohmic resistor may be used, for example, or also a transzorb diode. At least some of the induced countervoltage is passed to the electrical component taking up energy when the current acting on the coil ceases. Therefore, the magnetic field of the electromagnet which prevails during normal suction operation can be broken down within a very short period of time.

In one preferred configuration, a freewheeling diode and a Zener diode, which is polarized in the opposite direction to the freewheeling diode and is connected in series to it, are connected in parallel to the coil. As already explained, an induced countervoltage can be short-circuited via the freewheeling diode. Since this absorbs only a little of the energy originally stored in the coil, a Zener diode, which is polarized in the opposite direction, is connected in series to the coil. The Zener diode is, therefore, connected in a reverse direction with respect to the countervoltage of the coil generated by way of self-inductance and so a not inconsiderable voltage drops away at the Zener diode when the supply of current to the coil is switched off. The magnetic field of the electromagnet, which prevails during normal suction operation, can be returned practically to zero in a particularly short period of time by means of the Zener diode. As a result, the magnetic holding force, which keeps the valve member in its closing position when current acts on the coil, breaks down within a very short period of time and the valve member can lift away from the associated valve seat.

The Zener diode preferably has a breakdown voltage of more than 50 V. This has the advantage that the induction current of the coil can be returned practically to zero within a very short period of time by means of the Zener diode. The breakdown voltage of the Zener diode can, for example, be approximately 56 V.

The coil and the at least one component connected in parallel to the coil, i.e., for example, the freewheeling diode and the Zener diode polarized in the opposite direction to it, can preferably be connected to a source of AC voltage via an electrical switching unit and a rectifier unit. The electrical switching unit makes it possible to carry out the cleaning of the filter as a function of the drop in pressure at the filter and/or dependent on time. For example, it may be provided for a pressure sensor to be arranged both upstream and downstream of the filter and for the supply of current to the coil to be interrupted for a short time as a function of the pressures detected by the sensors in order to carry out cleaning of the filter. Alternatively, cleaning of the filter may be carried out at preferably uniform time intervals.

The electromagnet normally has an iron core, onto which the coil is wound. During normal suction operation, it may be possible for the iron core to be statically charged on account of dirt particles flowing past. The static charge can assume values which represent a hazard, in particular, for the electrical switching unit connected to the coil. As a result, the control of the electromagnet may be impaired. In one preferred configuration of the vacuum cleaner according to the invention, the iron core is, therefore, connected via a potential equalization line to a reference potential predetermined externally.

The reference potential can be earth potential or also an external DC or AC voltage potential. The potential of the iron core can be balanced with the external reference potential via the potential equalization line. As a result, a static charging of the iron core, which impairs the control of the electromagnet, is avoided. In particular, a very short-time interruption of the supply of current to the electromagnet can be impaired by a static charging of the iron core.

It is favorable when the potential equalization line connects the iron core to a mains voltage supply connection, wherein at least one ohmic resistor is connected into the potential equalization line. The ohmic resistor preferably has resistance values of at least 10 MΩ, in particular, resistance values of approximately 15 to 25 MΩ.

It is of particular advantage when at least two ohmic resistors with different resistance values are connected into the potential equalization line in series to one another. As a result, a first ohmic resistor can, for example, have a resistance value of approximately 8 MΩ and a second ohmic resistor can have a resistance value of approximately 12 MΩ. The use of different ohmic resistors has the advantage that during assembly of the vacuum cleaner the risk is reduced of two low-impedance resistors being used by mistake. The electrical safety of the vacuum cleaner is improved as a result.

The movable valve member is held reliably in its closing position with the aid of the electromagnet used in accordance with the invention. In order to open the closing valve, the supply of current to the electromagnet is interrupted for a short time. It is of advantage when the electromagnet is arranged on a valve holding device which forms the valve seat and when the valve member has a magnetizable element which is associated with the electromagnet and forms a magnetic circuit with the electromagnet in the closing position of the valve member. The magnetizable element, for example, an iron-bearing plate bundles the field lines of the electromagnet in the valve member so that it is kept reliably in its closing position due to the action of the magnetic holding force. If the valve member is, however, at a relatively slight distance of, for example, two millimeters from the valve seat, the magnetic circuit is interrupted since the magnetizable element is also at a corresponding distance in relation to the electromagnet. As a result, the holding force exerted by the electromagnet has only a very short range. During an opening movement, the valve member thus experiences a magnetic holding force only in the immediate area of the valve seat; the magnetic force is already so slight at a distance of approximately 2 mm between the electromagnet and the magnetizable element that it cannot return the valve member to its closing position. On the contrary, the closing spring is used to return the valve member.

As already explained, it can be ensured by means of the at least one component which is connected in parallel to the coil and takes up at least some of the energy stored in the coil that the magnetic holding force ceases within a very short period of time, for example, within ten milliseconds when the supply of current to the electromagnet is interrupted. As a result, a short-time opening movement of the valve member can be achieved which is held in its closing position preferably with the aid of the magnetizable element on the electromagnet. It is of advantage when, in the closing position of the valve member, the magnetizable element abuts on the end side of the electromagnet, thereby forming a gap of air. It has been shown that the influence of a residual magnetization of the magnetizable element on the opening movement of the valve member can be kept particularly small by making a gap of air available between the magnetizable element and the electromagnet. Such a residual magnetization would result in the valve member still being held, first of all, on the electromagnet on account of the magnetization of the magnetizable element which has taken place, despite a drop in the magnetic holding force of the coil. Such a residual magnetization can be counteracted, for example, by a special alloy of the magnetizable element. This does, however, entail not inconsiderable costs. Instead of using such an alloy, a gap of air between the magnetizable element and the electromagnet is provided in accordance with the invention. It has been shown that a very short-time opening movement of the valve member can be achieved due to such a gap of air being made available.

The gap of air is preferably narrower than 1 mm. It can, for example, be less than 0.7 mm, in particular, approximately 0.5 mm.

A particularly effective cleaning of the filter is achieved in one preferred configuration of the vacuum cleaner according to the invention in that the supply of current to the coil can be interrupted several times one after the other for a period of time of at the most 0.2 seconds at time intervals of less than 1 second. It may, for example, be provided for the supply of current to be interrupted two, three or even four times one after the other for approximately 100 milliseconds each at time intervals of approximately 0.5 seconds. The multiple, short-time interruption in the current results in the valve member performing a rapid opening and closing movement several times one after the other so that the at least one filter to be cleaned is acted upon with a pressure surge several times at short time intervals and has external air flowing through it. This results in an alternating mechanical load on the at least one filter, under the influence of which the filter or filters are cleaned effectively.

The supply of current to the coil can preferably be interrupted several times one after the other for less than 0.2 seconds at time intervals of approximately 10 to approximately 30 seconds. It may be provided, for example, for the supply of current to the coil to be interrupted for a short time at uniform time intervals of, for example, 15 seconds. The current can, in particular, be interrupted three times one after the other for approximately 0.1 seconds at intervals of 0.5 seconds each.

In one advantageous configuration, a flexible stop element is associated with the valve member and this acts on the valve member with a repulsion force in a position spaced in relation to the valve seat. A very short opening movement of the valve member can be achieved in a constructionally simple manner as a result of the flexible stop element, wherein the valve member is acted upon first of all only with the closing force of the closing spring, proceeding from its closing position. Only when the valve member has a certain distance in relation to the valve seat, will the flexible stop element become effective and act on the valve member with a repulsion force. The flexible stop element absorbs the movement energy of the valve member and accelerates it back in the direction of the valve seat. With the aid of the flexible stop element, the closing valve can be closed again within a very short period of time, in particular, after a period of time of less than 0.2 seconds. The normal suction operation of the vacuum cleaner can, as it were, be carried on continuously and, nevertheless, an effective cleaning of the filter can be achieved. External air enters the dirt collection tank only for a very short period of time and so the suction flow in the area of the suction inlet of the dirt collection tank is not noticeably interrupted. The vacuum cleaner is, consequently, characterized by a constructively simple construction, wherein all the filters present can have suction air flowing through them at the same time during suction operation and wherein the entire side of the at least one filter which faces away from the dirt collection tank can be acted upon with external air due to a short-time opening of the at least one closing valve. The external air is supplied to the filter in an impact-like manner, wherein the at least one suction unit is permanently in flow connection with the filter, i.e., also during the time of its cleaning.

The flexible stop element can be designed in different forms. It is preferably designed as a stop spring. This has a greater spring constant than the closing spring in one preferred configuration. The stop spring is, therefore, harder than the closing spring, i.e., a greater force is necessary to compress the stop spring than is the case for the closing spring. The stop spring can, like the closing spring, have a linear or also a non-linear characteristic. For example, it may be provided for the stop spring and/or the closing spring to become harder with increasing travel of the spring.

In one preferred configuration of the vacuum cleaner according to the invention, the closing spring and the stop spring are designed as helical springs with different diameters, wherein one of the two helical springs surrounds the other helical spring in circumferential direction. This makes a space-saving arrangement of the closing spring and the stop spring possible and, in addition, makes a simple assembly possible.

The closing spring preferably surrounds the stop spring in circumferential direction. This has the advantage that the valve member abuts on the closing spring at a relatively large contact surface and is guided back into the closing position by the closing spring. The tilting stability of the valve member is improved as a result.

The combined use of an electromagnet, in the freewheeling circuit of which at least one component taking up energy, for example, a freewheeling diode and a Zener diode, which is polarized in the opposite direction thereto, are connected in series to one another, with a closing spring which acts on the valve member permanently with a closing force and with a flexible stop element is of particular advantage since, as a result, the valve member can be reliably held in a sealing manner on the valve seat in its closing position and as a result of a very short-time interruption in the current the valve member can lift away from the valve seat for a period of time of less than 0.2 seconds on account of the difference in pressure acting on it and so the closing valve is opened. At a distance from the valve seat, the valve member meets the flexible stop element which acts on the valve member with a repulsion force in the direction towards the valve seat. As a result of the action of the repulsion force and the closing force exerted by the closing spring, the valve member again reaches the valve seat within a very short period of time. The closing spring has, in this respect, the function of returning the valve member to the area of the magnetic field of the electromagnet so that the valve member can be held on the valve seat during normal suction operation by the electromagnet which is again acted upon with current.

The vacuum cleaner can have several filters. It has proven to be particularly advantageous when the vacuum cleaner comprises a single filter. It may, in particular, be provided for the filter to be acted upon with external air over its entire surface area as a result of simultaneous opening of all the closing valves.

In a constructionally particularly simple configuration of the vacuum cleaner according to the invention, this merely has a single closing valve which is positioned on the side of a filter holding device with flow passages which faces away from the single filter. As a result of the closing valve being opened, the single filter is acted upon with external air over its entire surface area.

The configuration of the vacuum cleaner according to the invention makes it possible for external air to act on the side of the at least one filter, which faces away from the dirt collection tank, for a short time during normal suction operation and for this air to be removed by suction within a short time by means of the suction unit which is in flow connection with the filter even when the closing valve is opened. It is favorable when the valve member carries out a continuous movement back into its closing position via its open position, proceeding from its closing position, during the cleaning of the filter. With such a configuration, the valve member will, first of all, be accelerated powerfully in the direction away from the valve seat when the closing valve is opened and, subsequently, braked powerfully with the aid of the closing spring and, preferably, with the aid of the flexible stop element and reversed in its direction of movement in order to be accelerated again in the direction towards the valve seat. The entire movement of the valve member proceeding from its closing position via the open position back into the closing position can take place in fractions of a second, in particular, in a period of time of less than 200 milliseconds.

The at least one filter can preferably be acted upon with external air by means of the at least one closing valve whilst a vacuum is maintained in the opening area of a suction hose opening into the suction inlet. If the at least one closing valve is opened, the pressure on the side of the filter facing away from the dirt collection tank rises abruptly and is then reduced again. The abrupt rise in pressure causes an effective cleaning of the filter; since the rise in pressure does, however, drop again immediately due to the at least one suction unit, it does not lead to a complete interruption in the vacuum in the opening area of the suction hose opening into the suction inlet. On the contrary, a more or less continuous suction operation can be maintained.

The following description of one preferred embodiment of the invention serves to explain the invention in greater detail in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: shows a schematic sectional view of a vacuum cleaner according to the invention;

FIG. 2: shows an enlarged illustration of detail A from FIG. 1 and

FIG. 3: shows a block diagram of a supply circuit for an electromagnet of the vacuum cleaner.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, a vacuum cleaner 10 is illustrated schematically with a lower part which forms a dirt collection tank 12 and with an upper part 14 which is placed on the lower part and accommodates a suction unit 16. The dirt collection tank 12 comprises a suction inlet 18, to which a suction hose 20 can be connected. A suction nozzle can be connected to the free end of the suction hose 20 which is not illustrated in the drawings in order to achieve a better overview. Alternatively, it may be provided for the suction hose 20 to be connected to a machining tool, for example, a drilling unit or a milling unit so that dust which occurs during operation of the machining tool can be sucked in.

The upper part 14 forms a suction outlet 22 for the dirt collection tank 12. A folded filter 24 is held on the suction outlet 22 and an extraction line in the form of a suction channel 26 is connected to the filter. The folded filter 24 is permanently in flow connection with the suction unit 16 via the suction channel 26. The dirt collection tank 12 can be acted upon with a vacuum by the suction unit 16 via the suction channel 26 and the folded filter 24 and so a suction flow symbolized in FIG. 1 by the arrows 28 is formed, due to the action of which dirt can be sucked into the dirt collection tank 12. The dirt particles can be separated from the suction flow 28 by means of the folded filter 24.

A closing valve 30 is arranged in the upper part 14 above the folded filter 24 and is illustrated in FIG. 2 on an enlarged scale. It comprises a valve holding device 32 which is arranged stationarily in the upper part 14, forms a valve seat and interacts with a valve member in the form of a circular valve plate 34. The valve plate 34 is acted upon with a closing force in the direction towards the valve holding device 32 by means of a closing spring 36. The closing spring 36 has a linear characteristic and is clamped between the valve plate 34 and a plate-like filter holding device 38 which has a plurality of flow passages and is arranged stationarily in the upper part 14. The filter holding device 38 has an outer annular collar 40, which surrounds the adjacent end area of the closing spring 36 designed as a helical spring in circumferential direction, on its upper side facing the closing valve 30. The valve plate 34 has an annular bead 41, on which the closing spring 36 abuts on the outer side, on its underside facing the filter holding device 38.

In addition to the closing spring 36, the filter holding device 38 has a flexible stop element in the form of a stop spring 43 which, like the closing spring 36, is designed as a helical spring and has a linear characteristic. In order to hold the stop spring 43, the filter holding device 38 comprises on its upper side facing the closing valve 30 an inner annular collar 44 which is arranged concentrically to the outer collar 40 and in which the stop spring 43 engages with an end section. A guiding pin 46 is integrally formed on the valve plate 34 on the under side, aligned with the inner annular collar 44, this guiding pin being surrounded by an end area of the stop spring 43 in the closing position of the valve plate 34 illustrated in FIG. 2. The stop spring 43 is not subject to tensioning in the closing position of the valve plate, in contrast to the closing spring. Only when the valve plate 34 has lifted away from the valve seat of the valve holding device 32 will the stop spring 43 come to rest on the underside of the valve plate 34 and will be compressed somewhat during further movement of the valve plate 34.

The valve holding device 32 has a plurality of openings which are not illustrated in the drawings and which open into the valve seat, on which the valve plate 34 sealingly abuts when it takes up its closing position. At the level of the valve holding device 32, the upper part 14 has a lateral opening 48. External air can flow into the openings in the valve holding device 32 via the lateral opening 48. If the valve plate 34 takes up a position which is spaced in relation to the valve holding device 32 and, therefore, also in relation to the valve seat, the lateral opening 48 is in flow connection with the suction channel 26 via the openings in the valve holding device 32 and external air can act on the side of the filter 24 facing away from the dirt collection tank 12. If the valve plate 34 takes up its closing position, the flow connection between the suction channel 26 and the lateral opening 48 is interrupted.

In a central area, the valve holding device 32 has a magnetic holding device in the form of an electromagnet 50 with a magnetic core 51 which is surrounded by a magnetic coil 52. The end of the electromagnet 50 on the outer side is formed by a cylindrical casing 53 which, like the magnetic core 51, is produced from a magnetizable material. The casing 53 is surrounded in the circumferential direction by a guiding receptacle in the form of an annular space 55, in which a guiding sleeve 56 engages which is integrally formed on the valve plate 34 on the upper side. The annular space 55 and the guiding sleeve 56 form guiding elements for the displaceable mounting of the valve plate 34. The guiding sleeve 56 accommodates a magnetizable element in the form of an iron plate 58 which abuts on the free end side of the electromagnet 50 in the closing position of the valve plate 34 and forms a closed magnetic circuit in combination with the magnetic core 51 and the casing 53. The closed magnetic circuit bundles the magnetic field lines of the electromagnet 50.

The supply of current to the electromagnet 50 is illustrated schematically in FIG. 3. The magnetic coil 52 is in electrical connection with a rectifier unit 65 via a first current supply line 61 and a second current supply line 62, the rectifier unit being connected to mains connections 71 and 72 via a first connection line 67 and a second connection line 68. A source of AC voltage can be connected in a customary manner to the mains connections.

An electrically controllable switching unit 74 is connected into the first current supply line 61; the supply of current to the magnetic coil 52 can be interrupted with the aid of this switching unit as a function of a control signal which is made available by a control unit of the vacuum cleaner 10, which is not illustrated in the drawings, via a control connection 75 of the switching unit 74. A freewheeling diode 79 and a Zener diode 80 connected in series to one another are connected in parallel to the magnetic coil 52 in a free-running line 77, wherein the Zener diode 80 is polarized in the opposite direction to the freewheeling diode 79.

The magnetic core 51 and the casing 53 of the electromagnet 50 form a housing of the electromagnet 50 which is given the reference numeral 82 in FIG. 3. It is produced from an electrically conductive material, in particular, from an iron material and is in electrical connection with the first connection line 67 via a potential equalization line 84. A first ohmic resistor 86 and a second ohmic resistor 87 are connected into the potential equalization line 84 in series to one another. The resistance value of the first ohmic resistor is, for example, approximately 8 MΩ whereas the resistance value of the second ohmic resistor can, for example, be 12 MΩ.

The magnetic coil 52 can be acted upon with current via the rectifier unit 65 and the switching unit 74 for the purpose of forming a magnetic holding force which keeps the valve plate 34 in its closing position. The supply of current can be interrupted for a short period of time by means of the switching unit 74, for example, for a period of time of approximately 100 milliseconds. As a result, an induction voltage which is directed opposite to the original voltage is formed at the magnetic coil 52 as a result of self-inductance. This induction voltage will be short-circuited via the freewheeling diode 79 and the Zener diode 80 so that the associated induction current of the magnetic coil 52 drops away practically completely within a very short time, for example, within approximately 10 milliseconds after the supply of current has been switched off, i.e., within approximately 10 milliseconds the magnetic field of the electromagnet 50 which prevails during normal suction operation breaks down completely. The Zener diode 80 is polarized in the opposite direction to the freewheeling diode 79 and is, therefore, operated in a reverse direction so that the breakdown voltage, which is approximately 56 V in the embodiment illustrated, drops away at the Zener diode. As a result, a considerable amount of energy-can be removed from the magnetic coil 52 within a very short period of time and so the induced current drops away practically completely within the specified period of time of approximately 10 milliseconds.

If the user switches the vacuum cleaner 10 on, the suction unit 16 is started and, at the same time, the magnetic coil 52 is supplied with current via the switching unit 74 and the rectifier unit 65 so that the valve plate 34 is acted upon by the electromagnet 50 with a magnetic holding force which keeps it reliably in its closing position. The suction unit 16 acts on the dirt collection tank 12 and the suction channel 26 with a vacuum so that dirt particles, like drops of liquid, can be sucked into the dirt collection tank 12. Dirt particles are deposited at the filter 24 and so this gradually becomes clogged during normal suction operation. The supply of current to the magnetic coil 52 is therefore interrupted by means of the switching unit 74 several times for a short period of time at time intervals of, for example, 10 to 30 seconds, in particular, at time intervals of approximately 15 seconds. It may, for example, be provided for the supply of current to the magnetic coil 52 to be interrupted three times one after the other for approximately 0.1 seconds at intervals of 0.5 seconds each and for the normal suction operation to then be restarted for 15 seconds. The interruption in the supply of current results in the magnetic field of the electromagnet breaking down within a very short time, for example, within approximately 10 milliseconds on account of the use of the Zener diode 80 and, therefore, the magnetic holding force for the valve plate 34 ceases. On the other hand, this causes the valve plate 34 to lift away from the valve seat contrary to the action of the closing spring 36 on account of the difference in pressure acting on it which results from the external pressure of the external air present in the area of the valve holding device 32 and the internal pressure within the suction channel 26. External air can then flow into the suction channel 26 abruptly through the opening in the valve holding device 32. The filter 24 is, therefore, acted upon in an impact-like manner with external air on its side facing away from the dirt collection tank 12. This leads to a mechanical jarring of the filter 24. In addition, the filter 24 has external air flowing through it in a counterflow direction. This results, altogether, in an effective cleaning of the filter 24.

The valve plate 34 lifting away from the valve seat abuts on the stop spring 43, which acts on the valve plate 34 with a repulsion force in the direction towards the valve holding device 32, with its underside after a short lifting movement. The stop spring 43 absorbs the movement energy of the valve plate 34. The latter is accelerated by the stop spring 43 in the direction towards the valve seat. If the valve plate 34 approaches the valve seat, the stop spring 43 releases the valve plate 34. The latter is returned as far as the valve seat by the closing spring 36 so that the iron plate 58 again comes to rest on the end side of the electromagnet 50, wherein a gap of air of approximately 0.5 mm is formed, however, between the end side of the electromagnet 50 and the iron plate 58. If the iron plate 58 reaches the end side of the electromagnet 50, this is again acted upon with current via the switching unit 74 so that the valve plate 34 is again held sealingly on the valve seat by the electromagnet 50. The interruption in the supply of current for the electromagnet 50 takes place merely for a period of time of approximately 100 milliseconds so that the closing valve 40 opens only for a very short period of time and external air can reach the filter 24. Subsequently, the electromagnet 50 is again acted upon with current and the normal suction operation can be continued. On account of the short opening of the closing valve 30, a vacuum is also maintained during the cleaning of the filter in the opening area of the suction hose 20 opening into the suction inlet 18. As a result, a more or less continuous suction operation is possible for the user and, nevertheless, a reliable cleaning of the filter is guaranteed. 

1. Vacuum cleaner with a dirt collection tank having a suction inlet and being in flow connection with at least one suction unit via at least one filter and at least one extraction line, and with at least one external air inlet opening into the extraction line downstream of the at least one filter, said external air inlet being closable by means of at least one closing valve, wherein the at least one closing valve has a valve member movable back and forth between a closing position, said valve member abutting on a valve seat in said closing position, and an open position, said valve member being spaced from the valve seat in said open position, wherein said valve member is acted upon permanently by a closing spring with a closing force and in the closing position, in addition, by a magnetic holding device with a magnetic holding force, wherein the magnetic holding device comprises an electromagnet with a magnetic core and a coil adapted to be acted upon with current for the purpose of closing the closing valve, wherein at least one electrical component is connected in parallel to the coil, said component taking up at least some of the energy stored in the coil when the current acting on the coil ceases.
 2. Vacuum cleaner as defined in claim 1, wherein a freewheeling diode and at least one electrical component taking up energy and being connected in series thereto are connected in parallel to the coil.
 3. Vacuum cleaner as defined in claim 1, wherein a freewheeling diode and a Zener diode connected in-series thereto are connected in parallel to the coil, said Zener diode being polarized in an opposite direction to the freewheeling diode.
 4. Vacuum cleaner as defined in claim 3, wherein the Zener diode has a breakdown voltage of approximately 50 V.
 5. Vacuum cleaner as defined in claim 1, wherein the coil and the at least one component connected in parallel to the coil are adapted to be connected to a source of AC voltage via an electrical switching unit and a rectifier unit.
 6. Vacuum cleaner as defined in claim 1, wherein the magnetic core is connected via a potential equalization line to a reference potential predetermined externally.
 7. Vacuum cleaner as defined in claim 6, wherein the potential equalization line connects the magnetic core to a mains voltage supply connection, wherein at least one ohmic resistor is connected into the potential equalization line.
 8. Vacuum cleaner as defined in claim 7, wherein two ohmic resistors with different resistance values are connected into the potential equalization line in series to one another.
 9. Vacuum cleaner as defined in claim 1, wherein the electromagnet is arranged on a valve holding device forming the valve seat and wherein the valve member has a magnetizable element associated with the electromagnet, said element forming a magnetic circuit with the electromagnet in the closing position of the valve member.
 10. Vacuum cleaner as defined in claim 9, wherein in the closing position of the valve member the magnetizable element abuts on the end side of the electromagnet, thereby forming a gap of air.
 11. Vacuum cleaner as defined in claim 10, wherein the gap of air is narrower than 1 mm.
 12. Vacuum cleaner as defined in claim 1, wherein the supply of current to the coil is adapted to be interrupted several times one after the other for a period of time of at the most 0.2 seconds at time intervals of less than one second.
 13. Vacuum cleaner as defined in claim 1, wherein the supply of current to the coil is adapted to be interrupted several times one after the other for less than 0.2 seconds at time intervals of 10 to 30 seconds.
 14. Vacuum cleaner as defined in claim 1, wherein a flexible stop element is associated with the valve member, said stop element acting on the valve member with a repulsion force in a position spaced from the valve seat.
 15. Vacuum cleaner as defined in claim 14, wherein the flexible stop element is designed as a stop spring.
 16. Vacuum cleaner as defined in claim 15, wherein the spring constant of the stop spring is greater than the spring constant of the closing spring.
 17. Vacuum cleaner as defined in claim 15, wherein the closing spring and the stop spring are designed as helical springs with different diameters, wherein one of the two helical springs surrounds the other helical spring in circumferential direction.
 18. Vacuum cleaner as defined in claim 1, wherein the vacuum cleaner has a single filter.
 19. Vacuum cleaner as defined in claim 18, wherein the filter is adapted to be acted upon with external air over its entire surface area as a result of the closing valve being opened.
 20. Vacuum cleaner as defined in claim 1, wherein the valve member is movable continuously back into its closing position via its open position, proceeding from its closing position.
 21. Vacuum cleaner as defined in claim 1, wherein the at least one filter is adapted to be acted upon with external air by means of the at least one closing valve whilst a vacuum is maintained in the opening area of a suction hose opening into the suction inlet. 